Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

2. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Carbon dioxide

Freon

Brine

3. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Non-inflammable and toxic

Toxic

4. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

5. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Axial

Centrifugal

Piston type reciprocating

6. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Negative

Zero

None of these

7. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

None of these

Normal cooling

Super-cooling

8. The freezing point of sulphur dioxide is

-75.2°C

-56.6°C

-135.8°C

-77.7°C

9. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

10. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

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11. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Rankine

Carnot

Reversed Carnot

12. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

13. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

One heat exchanger

Three heat exchangers

14. The boiling point of ammonia is

-10.5°C

-33.3°C

-30°C

-77.7°C

15. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

16. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

1.33

3.33

2.33

17. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

18. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.6

0.376

0.67

19. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

20. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Any value

Low

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21. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

22. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Compressor and condenser

Condenser and receiver

Evaporator and compressor

23. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

24. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

25. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

High risibility with oil

Low boiling point

Large latent heat

26. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

27. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Absorber

Condenser

Evaporator

28. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

29. Rating of a domestic refrigerator is of the order of

5 tons

0.1 ton

10 tons

40 tons

30. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

30 bar

15 bar

Page 4 of 4

31. Which of the following cycles uses air as the refrigerant?

Ericson

Carnot

Stirling

Bell Coleman

32. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

1: 9

9: 1

33. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

34. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

35. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

36. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always more than unity

Always less than unity

Any one of the above

37. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

38. Most thermostatic expansion valves are set for a superheat of

20°C

10°C

15°C

5°C

39. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Water coolers

All of these

Room air conditioners

40. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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